Red tide is also called "red tide". Many people call it "red ghost". So what are the hazards of red tide? In recent days, red tide has broken out in many places in Fujian. Some seafood, especially shellfish, have been polluted. That is to say, after the suffering of green shellfish, the plain vegetables have also been lying on the gun. In Zhangzhou and Quanzhou, Shishi once suffered from poisoning due to people eating the plain vegetables by mistake.
It is the phenomenon that some bacteria, protozoa and phytoplankton in the water suddenly proliferate or highly aggregate under the specific environmental conditions, which causes the water discoloration.
What is the cause of red tide
1. Seawater eutrophication
As a result of the large amount of industrial wastewater and domestic sewage discharged into the sea, the nutrients are sub collected in the water body, resulting in eutrophication of the sea area. At this time, the contents of nutrients such as nitrogen and phosphorus, microelements such as iron and manganese, and organic compounds in the water increased greatly, which promoted the mass reproduction of red tide organisms. The results of red tide detection show that the water in the area where red tide occurs has been seriously polluted and eutrophicated. Nutrients such as nitrogen and phosphorus exceed the standard greatly. According to the research, some metals in industrial wastewater can stimulate the proliferation of red tide organisms. Adding iron chelator less than 3mg / dm3 and manganese chelator less than 2mg / dm3 to the seawater can make the red tide organism oodinoflagellate and eudinoflagellate reach the highest proliferation rate. On the contrary, in the seawater without iron and manganese elements, even under the most suitable temperature, salinity, pH and basic nutrition conditions, it will not increase the population density Secondly, some organic substances can also promote the rapid proliferation of red tide organisms. For example, the growth of gymnodinoflagellate is not obvious when it is cultured with inorganic nutrients, but when it is added with yeast extract, the growth is significant. When it is added with soil extract and vitamin B12, the growth of gymnodinoflagellate is particularly good.
2. Changes of Hydrometeorology and physical and chemical factors of seawater
The temperature of sea water is an important environmental factor for the occurrence of red tide, and 20-30 ℃ is the suitable temperature range for the occurrence of red tide. Scientists have found that a sudden rise in water temperature of more than 2 ℃ in a week is a precursor to the occurrence of red tide. The change of chemical factors such as salinity in seawater is also one of the reasons for the large-scale reproduction of the biological factor red tide organisms. Red tide may occur in the range of salinity 26-37, but thermocline and saltcline are easy to form in the range of salinity 15-21.6. The existence of thermocline and saltcline provides conditions for the aggregation of red tide organisms, which is easy to induce red tide. Because of the confluence of runoff, upwelling, water mass or current, the nutrients in the seabed rise to the upper layer of water, resulting in high eutrophication of coastal waters. The content of nutrients increased rapidly, which resulted in a large number of diatoms. The overgrowth of these diatoms, especially the density of skeletoneae, often causes red tide. These diatoms provide abundant food for Noctiluca, promote the rapid proliferation of Noctiluca, and form pink Noctiluca red tide. According to the monitoring data, when the red tide occurs, the water area is mostly dry and less rain, the weather is sultry, the water temperature is high, the wind is weak, or the tide is slow.
3. Self pollution of mariculture
With the rapid development of coastal aquaculture in China, especially the rapid development of shrimp aquaculture. There are also serious problems of self pollution. In prawn culture, a large amount of compound feed and fresh bait are fed manually. Due to the old and imperfect culture technology, the quantity of baits is often large, and the amount of residual baits in the pond is increased, which seriously pollutes the water quality of culture. On the other hand, because the shrimp pond needs to drain and change water every day, a large number of sewage is discharged into the sea every day. These water with a large amount of residual bait and feces contains ammonia nitrogen, urea, uric acid and other forms of nitrogen-containing compounds, accelerating the eutrophication of the sea water, thus providing a suitable biological environment for the red tide organisms, accelerating their proliferation, especially in the high temperature, sultry and windless environment Red tide is most likely to occur under the condition of. It can be seen that the frequency of red tide also increases due to the self pollution of mariculture.
What are the hazards of red tide
A large number of red tide organisms gather in the gills of the fish, causing the fish to suffocate and die due to lack of oxygen. After the death of red tide organisms, the algae consume a large amount of dissolved oxygen in the water in the decomposition process, which will also cause the fish and other marine organisms to die due to lack of oxygen. The bodies of these marine organisms will release a large number of harmful gases and toxins in the decay process, which will be serious in the infinite cycle of death process The pollution of the marine environment causes serious damage to the normal marine ecosystem. After the occurrence of red tide, in addition to the discoloration of the sea water, the pH value of the sea water will also increase, the viscosity will increase, and the plankton of non red tide algae will die and decay; red tide algae also die in large numbers due to explosive proliferation and excessive aggregation.